UVB irradiation and distribution of arachidonic acid (20:4) and stearic acid (18:0) in human keratinocytes

Abstract

Human keratinocytes (NCTC 2544) in culture were labeled with either 14C-arachidonic acid or 14C-stearic acid and then exposed to UVB irradiation (9 or 90 mJ/cm2). Exposure of the keratinocytes to UVB irradiation resulted in considerable rearrangement of the membrane fatty acids. Following UVB irradiation the percentage amounts of 14C-arachidonic acid and 14C-stearic acid were significantly decreased in phospholipids, in phosphatidylethanolamine and in phosphatidylcholine. The liberation of stearic acid from phospholipids was accompanied by accumulation of radiolabel into the culture medium, but in 14C-arachidonic acid-labeled cells the amount of radiolabel in the culture medium was not changed following UVB irradiation despite liberation of arachidonic acid from phospholipids. It seems evident that, following UVB irradiation, the rate of reincorporation of liberated 14C-arachidonic acid, a polyunsaturated fatty acid, is higher and thus different from that of a saturated fatty acid, 14C-stearic acid. The present study suggests that exposure of keratinocytes to UVB irradiation is followed by liberation of both saturated and unsaturated fatty acids and also considerable reacylation of the unsaturated fatty acids.